| Daspletosaurins | |
|---|---|
 | |
| Skeletal mount ofDaspletosaurus torosus | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Superfamily: | †Tyrannosauroidea |
| Family: | †Tyrannosauridae |
| Subfamily: | †Tyrannosaurinae |
| Tribe: | †Daspletosaurini Voris et al., 2020 |
| Type species | |
| Daspletosaurus torosus Russell, 1970 | |
| Genera | |
Daspletosaurini is an extinctclade (tribe)[1][2] oftyrannosaurine dinosaurs that lived inLaramidia during theLate Cretaceous (MiddleCampanian) period. It consists of two genera:Daspletosaurus andThanatotheristes. Four species have been described in the two genera, namelyDaspletosaurus torosus,Daspletosaurus horneri,Daspletosaurus wilsoni, andThanatotheristes degrootorum. At one point all of them were assigned as specimens ofD. torosus, but several papers since 2017 have found them to represent distinct species. Some researchers foundanagenesis in the group, whether contained in a daspletosaurin clade or paraphyletic in respect to the lineage of tyrannosaurines leading up toTyrannosaurus,[3][4][5] but a 2023 study refuted this theory on the basis of morphological and stratigraphical data.[6]
Daspletosaurins were large predators, reaching around 9 metres (30 ft) in length.[3] However, they were not the largest tyrannosaurids, as more derived taxa, such asTyrannosaurus, could reach lengths of more than 12 metres (39 ft).[7]
Daspletosaurini is diagnosed by characteristics such as the presence of an extremely coarse subcutaneous surface of the maxilla anteroventral to the antorbital fossa; a constricted jugal ramus of maxilla; the anteroventral corner of the maxilla tapers into a shallow angle (<65°) as measured between the alveolar margin of the first two alveoli and the anterior margin of the subcutaneous surface; a prefrontal that is broad in dorsal view and strongly dorsomedially arced in anterior view; a dentary chin located ventral to either the third alveolus or third interdental plate and possessing no fewer than 14 maxillary teeth.[4]
In the 2020description ofThanatotheristes, Voris et al. erected Daspletosaurini as a new clade within Tyrannosauridae, as a sister taxon to a clade comprisingZhuchengtyrannus,Tarbosaurus, andTyrannosaurus. Thecladogram below shows the results of thephylogenetic analyses performed by Voris et al. (2020):[4]
In 2022, Warshaw & Fowler proposed that the threeDaspletosaurus species evolved throughanagenesis in the Tyrannosaurinae in a line leading toZhuchengtyrannus,Tarbosaurus, andTyrannosaurus. Due to their more fragmentary nature,Thanatotheristes andNanuqsaurus were excluded from this analysis. The cladogram below shows the results of the phylogenetic analysis performed by Warshaw & Fowler (2022).[5]
| Tyrannosaurinae |
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In 2023, Scherer and Voiculescu-Holvad argued that the stratigraphic ranges ofD. torosus,D. wilsoni and an unnamed species from theDinosaur Park Formation andOldman Formation show a clear overlap, indicating that anagenesis may not be the predominant factor of speciation within the genus, since all species ofDaspletosaurus were contemporaneous with each other at some point during its evolution. Phylogenetic analyses resolvedD. horneri as the most basal species, in spite of the fact that it's stratigraphically the youngest. While the authors did not completely refute the possibility that anagenesis was the main driver ofDaspletosaurus evolution based on the intermediate morphological features, they also suggested thatD. wilsoni may be a junior synonym ofD. torosus, since there is a near lack of autapomorphic characters that can differentiate this species. They also claimed thatDaspletosaurus did not evolve fromThanatotheristes, since they found no support on the basis of morphological and stratigraphical data, and that anagenesis will not be supported unequivocally due to the limited sample and nature of the fossil record which doesn't show a great degree of variation in morphology. The cladogram presented for their phylogenetic analysis is shown below.[6]
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